Hayden is the foreman on a three-unit apartment building under construction high on the hill. Buildings under construction must have outhouses, and outhouses have become a target of the most bizarre, least fragrant series of arsons in San Francisco history.

Over the last two months, in the dead of night, 14 outhouses have been set ablaze around Russian Hill. On Thursday, another outhouse burned at Union and Franklin streets - not technically on Russian Hill - which means that the arsonist has, in the great tradition, undertaken a Western Expansion.

Weeks ago, Hayden realized the outhouse on his construction site wasn't safe, not even with a fancy four-digit brass combination padlock protecting it.

"So I had an epiphany," he said.

He covered the bright green plastic outhouse on two sides with dark plywood so that it looked like a storage shed. On the third side he hung a brown blanket, to make it blend in with the hillside. Only a very sharp-eyed passer-by could pick out the potty among the surrounding construction equipment.

"It's smoke and mirrors," he said. "I've been in the business for 40 years, and doing this was a first for me."

So far, the ruse has worked. A week ago, the arsonist bypassed Hayden's disguised toilet and struck another outhouse directly next door. That outhouse was destroyed, and a tall tree next to it was badly burned, but the flames did not spread to the two-story home only 3 feet away.

For two months, the hill has been very, very lucky. The outhouse torchings are Russian roulette - with disaster possible at any time.

"Sooner or later, if this guy isn't caught, there's going to be a major fire," Hayden said. "The longer this guy is out there, the more dangerous it is."

The string of arsons has caused a revolution in the business of portable toilets.

Typically the toilets are leased, for $100 or so per month, and the renter is responsible for damage. But Mill Valley Refuse, which supplied the burnt toilet and its replacement next door to Hayden's construction site, said the Russian Hill crisis made the company feel obliged to begin issuing outhouse insurance for an additional $5 a month, to protect its customers from being on the hook for the price of a new potty, which costs around $1,000.

"This is something new in the industry," said Rebecca Henderson, portable toilet administrator for the company. "But we're taking these arsons to heart. You get attached to portable toilets. They're your business, and you don't want to see anything happen to them, or to your customers."

Police and firefighters have stepped up nightly potty patrols, although authorities concede they cannot be everywhere at once.

And residents are trying to figure out what it all means and what they can do about it.

"I think it's somebody trying to make a statement about outhouses," said antique shop owner Mark Busacca, owner of the Busacca Gallery at Hyde and Union streets. "They're big and ugly, and they sit out in the street."

Fortunately, he said, there are no outhouses in the immediate vicinity of his gallery, or his most prized treasures - including a priceless shield made of hippopotamus hides - could be lost to the ages.

On Hyde Street, Julie Whitmer was walking her dog, Sierra, and pondering the nature of outhouses.

"They're unattractive, but temporary," she said. "Whoever's doing this is probably a young person, with not enough to do. That's my guess."